Wafer-Level Packaging (WLP) refers to the technology of packaging an integrated circuit at wafer level, instead of the traditional process of assembling the package of each individual unit after wafer dicing. Wafer-level packaging is essentially a true chip-scale packaging (CSP) technology, since the resulting package is practically of the same size as the die. Wafer-level packaging consists of extending the wafer fabrication processes to include device interconnection and device protection processes. In many cases, redistribution layer and bump technology is used to facilitate the packaging.
Wafer-level packages using bump technology extend the conventional wafer fabrication (“fab”) process with an additional step that deposits a multi-layer thin-film metal rerouting and interconnection system to each device on the wafer. The interconnection system is achieved using the same standard photolithography and thin film deposition techniques employed in the device fabrication itself.
The additional level of interconnection redistributes the peripheral bonding pads of each chip to an area array of under bump metallization (UBM) pads that are evenly deployed over the chip's surface. The solder balls or bumps used in connecting the device to the application circuit board are subsequently placed over the UBM pads. Aside from providing the WLP's means of external connection, use of redistribution layer and bump technology also improves a respective chip's reliability by allowing the use of larger and more robust balls for interconnection, resulting in better thermal management of a semiconductor device's input/output (I/O) system.
Bumped die configurations, particularly those including WLP technologies, face increasing pressure to deposit more I/O capability per a specific area. In general, however, the specific area in which to deposit bumps has been traditionally limited.